Research at Aberystwyth into qualitative simulation of electrical circuits has been
word-leading for nearly two decades. During that time, the Advanced Reasoning
Group has developed a variety of electrical circuit simulators. The most successful,
CIRQ, has been deployed for more than ten years in industrially useful design
analysis systems, and has undergone a range of improvements over that time.
MCIRQ is a more advanced version of CIRQ that was developed on the Design for
the Whole Vehicle, Whole Lifecycle EPSRC Project at Aberystwyth. It is able to
reason about circuits with multiple levels of qualitative resistance, and to indicate
the different levels of current activity in the circuit. It showed great promise of
being able to assist the design analysis systems in producing improved analysis
reports, but was never deployed industrially because it was not able to analyse as
wide a set of circuits as the original CIRQ software.
This thesis describes a reimplementation of MCIRQ for use with both electrical
and
fluid
flow systems. It extends the theory of electrical qualitative analysis in
several ways, and makes several improvements to the original version of MCIRQ:
It replaces the Forward-Reverse labelling system of path finding with Series-
Parallel reduction system to determine current magnitude and direction.
It improves the Star-Delta Reduction algorithm to deal with problem cases
that do not occur in well-formed electrical circuits, but which do occur in
the circuits with failure that are dealt with in failure analysis work.
It extends MCIRQ to deal with many bridge circuits that were impossible
to resolve in the previous version of MCIRQ.
It introduces a principled strategy for resolving the direction of current
flow
within the circuit.
The overall effect of these improvements is to transform MCIRQ into a qualitative
analysis tool that can be used for real world applications. The thesis illustrates
the kinds of analysis that can now be done by MCIRQ that was impossible before.
The new MCIRQ has been employed on the ASTRAEA project. It has made
possible applications of design analysis for engineering systems that could not have
been addressed by any of the previous circuit analysers, notably in the domain of
systems with both electrical and hydraulic aspects.

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